So, I'm not too worried about this, I just want to fix it for next time.

I brewed a second batch of Belgian Wit on Saturday to the exact same recipe I used last month.

Last time: Mashed at 154 for 1 hour. Only lost 1 degree over the hour.

This time:

I brought my mash water to the exact same temp as last time, still accounting for the temp drop after grains are added. This time, though, my temp only came out to 152. After the hour mash, I was shocked when my temp was reading 143!

This, along with the fact that I may have runoff too much of my mash into the kettle, is what I believe caused my low gravity. I just wanted to get some other feedback.

Last time, my gravity was right on target at 1.052. This time, I measured at 86 degrees and it was at 1.035. I'm guessing, but I think that puts me at around 1.040 after adjusting the hydrometer for the high temp.

It's possible you measured a hot spot and got a high temp, when it was a bit low. A low mash temp can take longer to finish, but if it averaged in the mid to high 140's, it should have finished in an hour. But maybe not.

It's also possible that the grain crush wasn't the same. If you used the LHBS mill, someone might have changed the adjustment. If you used your own mill, you can check to see if the setting slipped.